Several kinds of union joints are known, a connecting end of which is respectively provided with, for example, a straight or bent pipe joint having a screwing part, a flange part, an insertion or nipple part, a receptacle or socket part, another union part and the like. These connecting ends shall be made strong with a shape having a diameter equal to or larger than that of the union swivel end, so that connecting ends shall be constructed without usual fastening means such as screws, weldings, ring-couplings which were used to pass a union nut over the union swivel end before the union joint is assembled. Any interfaces which were included to assemble divided parts into a unit device should be deleted to increase strength and durability.
A prior union joint which has a flange type connecting end 3 in FIG. 1 used screw means 7a and 7b for allowing the union nut 4 to pass on a union sleeve 7 over the union swivel end 5 before the flange connecting end 3 will be assembled with the screw means 7a and 7b. In this, the screw 7a was provided on the center hole of the flange part 3, and a paired screw 7b was on the end of the union sleeve 7. A radial engagement section may be thus provided between the union nut 4 and the union swivel end 5 as required. The radial engagement section is determined by a difference between an inner diameter D1 of the union nut hole and an outer diameter d1 of the union swivel end 5. The union joint 1 thus constructed can screw the union nut 4 on a screwing end of a ball valve 2. However, it has a weak point at the screwed means 7a and 7b, at which cracking 10 took place, especially on the union sleeve 7, because thrust load which acts on the flange part 3 as vibrational, expandable or contractive force increases concentratively internal stresses at the base of screw flange part 3. Such construction is disclosed, for example, in Japanese Utility Model Open Publication Nos. 127477/81 and 144783/81.
FIG. 2 shows another prior union joint in which a split ring 14 is used in place of the structure of a union swivel end to product it with a flange type connecting end 3 and the union sleeve 7 made in a unit. To use split ring 14, the forward end section of the union sleeve 7 is worked to provide a groove 15 and a peripheral protrusion wherein the split ring 14 is occupied in the groove 15 and is supported by the peripheral protrusion. An outer diameter d2 of the peripheral protrusion is smaller than the outer diameter D1 of the union sleeve 7, so that the union nut 4, first and then the split ring 14 are inserted on the union sleeve 7 in order from the forward end. After such insertion, the split ring 14 is inserted by hand in the groove is and engaged by the peripheral protrusion so as to assemble the union joint 1. However, the weak point would be shifted and would appear at the split ring 14 or the periphral protrusion from the base of the flange connecting part 3. Durability also decreased in this assembly between the union swivel end 5 and the split ring structure 14. The resulting force facilitates the split ring 14 and/or the small peripheral protrusion being damaged, distorted or expanded to disengage themselves.
From such experience, an ideal structure was desired and resulted in the structure of FIG. 3 in which usual fastening means such as screw, threaded, welded, or splitted means is not used to construct the union joint. Further prior are related to this, is disclosed in, for example, Japanese Patent or Utility Model Open Publication Nos. 99,261/78 and 25,635/84.
As shown in FIG. 4a, a union nut 4 which was previously produced with the union screw is screwed with a splittable die block 16 of a hollow shape, and a bisectional mold 19 is assembled to include the combined union nut 4 and die block 16 for forming a molding space from which a union swivel end and a flange connecting end will be produced in a unit union sleeve, as shown in FIG. 4(a). A conduit pass of the union joint is made by insertion of two pins 18, 18 into the assembled bisectional mold 19. Molten synthetic resin is thereafter injected into the resultant cavity 20, and an ideal union joint may be obtained after the splittable die block 16 was removed from the union nut 4 and the resulting union sleeve during removal of the used bisectional mold 19.
An expensive cost has resulted from this prior art procedure due to complicated mold assembly and operation. Another unreasonable difficulty was that the union sleeve was required to have an axial length two times the axial length of the union nut 4, inasmuch as the splittable die block 16 can be removed between the resultant union swivel end and the union nut 4. The requirement of this longer sleeve induces wasteful material cost or decreased durability from the union joint. This drawback may be avoided according to the prior art referring to FIG. 4(b).
Some modification onto the above resulted in formation of partial cavity which remains between the union nut 4 and the splittable die block 16 screwed in the nut. However, there still remains many interfaces in the thus assembled mold, additionally including the screwed interface, which is exposed to the partial cavity for forming the union swivel end. Cost increases also resulted due to work finishing for removal of many complicated flashes. The resulting efficiency was too small to increase use of the injection machine and the many mold parts required because of their complexity.